Get Oriented in an Unfamiliar Codebase

Background: I've just joined a native [iOS / Android] project I didn't
write. Stack: [Swift/SwiftUI/UIKit or Kotlin/Compose/Views], [minimum OS
version], [rough app size: screens, modules, contributors]. Here is the
project structure and a few key files:

[Paste the directory tree, the app entry point, and one or two
representative feature folders]

Use case: Help me build an accurate mental model of this app fast, so I
can make my first change without breaking something I can't see.

Implementation details:
- Identify the architecture actually in use, not the one the folder names
  claim—call out where the codebase is inconsistent with itself
- Trace how data flows from the network or database up to a rendered screen
- Point out the seams: where is dependency injection wired, where does
  navigation get decided, where is global/shared state kept
- Flag anything that looks load-bearing and fragile

Deliverable: A written orientation covering (1) the architecture as
practised, (2) an annotated data-flow walkthrough for one representative
screen, (3) the five files I should read first and why, and (4) a list of
questions I should ask the team that the code alone can't answer.